High-frequency surgery has been used for many years in both human and veterinary medicine to coagulate and/or cut biological tissue. Hereby, suitable electrosurgical instruments are used to direct high-frequency (“HF”) current through the tissue to be treated so that it changes as a result of protein coagulation and dehydration. The tissue contracts in such a way that the vessels are occluded and bleeding stopped. A subsequent increase in the current density achieves an explosion-like vaporisation of the tissue fluid and the ripping open of the cell membranes, wherein the tissue is completely transected.
Both bipolar and monopolar techniques are used for the thermal treatment of biological tissue. With monopolar arrangements, the HF current supplied by the HF generator to the electrosurgical instrument is applied to the tissue to be treated via an active electrode, wherein the current path passing through a patient's body travels to a neutral electrode and from there back to the HF generator. A high current density per unit of area to be treated is provided at the active electrode, while the current density per unit of area at the neutral electrode is much lower than that at the active electrode. This is achieved by means of a suitably large-area design of the neutral electrode. This is the only way to guarantee that no damage, such as burning, for example, occurs to the tissue on the passage of the current from the tissue to the neutral electrode.
Bipolar instruments with two electrode parts electrically insulated from each other are also increasingly gaining in importance. This means the current path between the electrode parts can be calculated and does not travel long distances through the patient's body. This reduces the influence of, for example, cardiac pacemakers or other devices connected to the patient during an operation.
Monopolar technology is in particular suitable for interstitial coagulation if a current that passes uniformly (e.g., with radial symmetry) through the tissue to be treated, i.e., through the target tissue, is required for the treatment. This enables the treatment of e.g., tumours or metastases in that the electrosurgical instrument suitable for the monopolar coagulation is inserted (stuck) into the tissue to be treated, for example into a tumour, and the destruction of the tumour (tumour devitalisation) is initiated by the application of the high-frequency current, that is by the coagulation.
Coagulation and/or a cutting process is performed using HF surgical devices comprising an HF surgical device with an HF generator to generate a high-frequency voltage, and hence a high-frequency alternating current, and switching devices and/or a control and regulating device to activate or deactivate the HF generator.
With monopolar coagulation, in particular with interstitial coagulation, but also with cutting processes, up to now it has not been possible to determine or assess the size of a coagulation zone in advance, since coagulation cannot be controlled in this regard. Instead, the size of the expected coagulation zone has to be estimated on the basis of empirical values and/or monitored using imaging techniques.
However, working exclusively with empirical values requires an increased safety factor to be observed with regard to the amount of energy to be introduced into the tissue. It is only with an excess of energy—together with the high stress this places on the tissue surrounding the target tissue—that the risk of incomplete coagulation, and hence incomplete devitalisation of the target tissue, can be avoided. Neither does the use of imaging techniques represent a satisfactory solution. On the one hand, imaging techniques are extremely complicated and cost-intensive, on the other hand, they cannot in principle be used with an HF current application.
The invention is therefore based on the object of further developing an HF surgical device of the type described above such that coagulation processes and/or cutting processes are optimised and can be monitored in an extremely simple way.